Extended monopole spectrometers and filters

ABSTRACT

In a monopole mass spectrometer the conventional angle electrode and hyperbolic cylindrical electrode are replaced by an electrode consisting of a hollow or solid circular cylindrical electrode surrounded by a hollow square cylindrical electrode. This provides the possibility of dividing the circular cylindrical electrode into 2, 3 or 4 parts by an insulating structure which may or may not be vacuum sealed to the surrounding square cylindrical electrode, thereby enabling a number of ion beams to be mass filtered simultaneously by only two analysing electrodes. It also offers the possibility of utilising the hollow square cylindrical electrode as a portion of the vacuum containment vessel for the mass spectrometer.

Unite States Patent [191 Hiller et al.

1 EXTENDED MONOPOLE SPECTROMETERS AND FILTERS [75] Inventors: John BarryHiller, Thornleigh; John Alan Richards, Townsville; Richard MeredythHuey, Sylvania, all of Australia [73] Assignee: Unisearch Limited,Kensington,

Australia [22] Filed: June 28, 1973 [21] Appl. No; 374,369

[30] Foreign Application Priority Data Dec. 9, 1975 PrimaryExaminerJames W. Lawrence Assistant Examiner-B. C. Anderson Attorney,Agent, or Firm-Browdy and Neimark [571 I ABSTRACT In a monopole massspectrometer the conventional angle electrode and hyperbolic cylindricalelectrode are replaced by an electrode consisting of a hollow or solidcircular cylindrical electrode surrounded by a hollow square cylindricalelectrode. This provides the possibility of dividing the circularcylindrical electrode into 2, 3 or 4 parts by an insulating structurewhich may or may not be vacuum sealed to the surrounding squarecylindrical electrode, thereby enabling a number of ion beams to be massfiltered simultaneously by only two analysing electrodes. It also offersthe possibility of utilising the hollow square cylindrical electrode asa portion of the vacuum containment vessel for the mass spectrometer.

13 Claims, 10 Drawing Figures .5. Patent Dec. 9, 1975 Sheet 10f33,925,663

US. Patent Dec. 9, 1975 Sheet 2 of3 3,925,663

FIG Lb US. Patent Dec. 9, 1975 Sheet 3 of3 3,925,663

of a hollowor solid circular cylindrical electrode sur-' rounded by ahollow squarecylindrical electrode. The circular cylindrical electrodemay' in certain forms of the invention be divided into 2, 3 or 4segments or quadrants by an insulating structure which may or may notextend to the hollow square cylindrical electrode.

In order that the nature of the invention may. be better understood,preferred forms thereof are'hereinafter described by way of example withreference to the accompanying drawings in which: a

FIG. 1 is anend view of a conventional monopole spectrometer;

FIG. 2 is an exploded isometric sketch of a fourfold monopole massspectrometer incorporatinganalyzing electrodes according totheinvention,

FIG. 3 is an end view of the basic form of analyzing electrodesaccording to the invention,

FIG. 4a is a similar view of a further form of the invention in whichthe circular cylindrical electrode is divided into four quadrants by aninsulating structure which extends to and is vacuum sealed to the hollowsquare cylindrical electrode, a

FIG. 4b is a similar view of a further form of the invention similar tothat of FIG. 4a in which the insulating structure does not extend to thesquare cylindrical electrode,

FIG. 5a is a similar view of a further formof the invention in which thecircular cylindrical electrode is divided into two semi-circularsegments by an insulating structure.

FIG. 5b is a similar view of a still further form of the invention inwhich the circular cylindrical electrode is divided into three segmentsby an insulating structure and,

FIGS. 6, 6a and 6b illustrate the manner in which spatial extensions andduplications of the structures shown in the figures referred to abovemay be arranged.

The monopole mass spectrometer, originally proposed by von Zahn (U.VONZAHN, Monopole Spec- FIG. 2 more than is necessary for anunderstanding of the present invention.

In-FIG. 2 a central circular section cylindrical electrode is indicatedat 1 and this is supported in the center of a square cylindrical boxelectrode 2 the space between the electrodes being evacuated, At one endof the assembly is a'suitable means for ionizing and inject ing agaseous sample into four channels of the fourfold monopole structure,which are constituted by the spaces defined between the cylindrical rodelectrode and the four corners of the box electrode 2. A suitabletrometer, A New Electric Field'Mass Spectrometer,

Rev. Sci. Inst., 34, (1963), 1-4) and the device which is termedconventional in this specification, has analyzing electrodes whichconsist of an angle electrode A and a hyperbolic cylindrical electrode Bconnected to a source C of potential of, for example, the form g(t) =-U-Vcos t as shown in FIG. 1 of the accompanying drawings. In the mode ofoperation commonly employed the angle electrode A is held atelectrically zero, or earth, potential whilst the hyperbolic cylindricalelectrode B is driven by a constant potential to which has been added asinusoidal potential. Alternatively,

the hyperbolic cylindrical electrode can be supplied with any othersuitably periodic high frequency waveform.

FIG. 2 shows a fourfold monopole mass spectrometer in a purelydiagrammatic form illustrating the use of an electrode configurationsimilar to that shown in FIG. 3 and described below. As the presentinvention is concerned purely with the configuration of the analyzingelectrodes and as the structure and functioning of mass it is notproposed to describe the arrangement shown in time varying voltagegenerator for exciting the cylindrical rod electrode 1 is indicated at 4and 5 indicates a vacuum sealed electrical feed-through through whichconnection is made to the electrode 1. 6, 7, 8, and 9 represent the ionbeams to be analyzed. Four Faraday cup collectors 10, 11, 12 and 13serve to detect the stable ion currents in each of the four monopolechannels of the fourfold monopole structure which originate from theionfbeams 6, 7, 8 and 9-. The output from this latter is led by means ofa vacuum sealed electrical feed-through 16 to a suitable currentmeasuring instrument 14 such as an electrometer amplifier. The portiontrodes of the monopole mass spectrometer can be extended with resultingimprovements in performance and/or increases in versatility andflexibility, thereby leading to a new class of monopole device..lnherentin the evolution of this new class is the approximation of thehyperbolic cylindrical electrode by a circular cylindrical electrode ofa suitable diameter. This approximation is common place for thequadrupole mass spectrometer. Having made this approximation the angle.electrode A of FIG. 1 can be extended into a hollow square cylinder asshown, for example in FIG. 3,

, thereby causing the circular cylindrical, or rod, electrode 17 to beshared in common by the four angle electrodes l8, 19, 20 and 21 soformed. This creates, with only two analysing electrodes, a structurethrough which four ion beams can be mass filtered simultaneously as willbe appreciated from a consideration of FIG. 2. When these four beams arefed from a common ion source such as 3 of FIG. 2 and are terminated by acommon ion detector (Faraday cup collectors 10, ll, 12 and 13 of FIG. 2)a monopole-based mass spectrometer is produced which has a sensitivityof four times that of the conventional monopole mass spectrometer.

In addition to improved sensitivity a further feature of the structurejust described, as with the following elaborations thereon, is thepossibility of using the surrounding square cylindrical electrode as aportion of the vacuum containment vessel for the mass spectrometer, asis the case in the arrangement shown in FIG. 2, thus leading to ananalyzing structure of physically small dimensions. An outcome of thisis the ease with which the structure may be pumped.

Another simplifying feature is the possibility of making the rodelectrode hollow thereby allowing electrical connections to the ionsource to be carried within it. This would permit all wiring to thedevice to be made via a rear mounted plate as is usual for present dayquadrupole devices.

Two elaborations of the above structure are shown in FIG. 4a and 4b inboth of which the single rod electrode 22 is segmented into fourquadrants separated by and mounted upon a cruciform electricallyinsulating arrangement 23 the extremities of which are vacuum sealed tothe box electrode 24. In the first configuration the insulatingstructure is shown extended so that the four monopole structures formedby the rod and box electrodes 22 and 24 may filter beams originating infour ion sources which in turn may be sampling either four separateinlets or one common inlet. Since the four quadrants of the rodelectrode are electrically isolated, each monopole structure may betuned to filter different masses by suitably adjusting either themagnitude of the periodic high frequency potentials (and DC. potentialsshould they be used) applied to the quadrants, which is to be preferred,or alternatively the frequencies of the periodic potentials. Fourseparate sources of potential g1 (t) to g4 (t) are indicated in thedrawing.

Inthe second configuration, shown in FIG. 4b the four quadrants of thesingle rod electrodeare again electrically insulated, however theinsulation 26 does not extend to the walls of the hollow box electrode27, thereby not requiring vacuum sealing at the intersections. Since theproperty of strong focussing will ensure that ions being transmitted bya quadrupole-based instrument will be constrained by electric forceslargely to the dielectric region between the electrodes, each quadrantmay be excited by suitably differing waveforms from sources gl(t) g4(t)thereby allowing the device to analyze one common sample for fourdiffering mass numbers.

The configuration shown in FIGS. a and 5b are subject to the samecomments as set out above and represent variations which may be founddesirable in certain applications. In these figures the broken lines atthe outer extremities of the insulators 28 and 29 indicate that thesemay either be continued to the hollow box electrodes 30 and 31respectively and vacuum sealed to them or not as desired.

As is illustrated in FIGS. 6a and 6b all the single electrodeconfigurations shown in FIG. 6 or any of those described above may beextended or duplicated to any desired extent.

We claim:

1. A monopole mass spectrometer comprising:

an analyzing configuration consisting of a circular cylindricalelectrode extending coaxially within a surrounding hollow-squarecylindrical electrode;

means for injecting ionized beams into said spec trometer between saidcircular cylindrical electrode and said square cylindrical electrode;

means for detecting said beams disposed opposite said injecting means;and

means for applying potential to both said circular cylindrical electrodeand to said hollow square cylindrical electrode.

2. The combination claimed in claim 1 wherein said circular cylindricalelectrode is hollow.

3. The combination claimed in claim 1 wherein said circular cylindricalelectrode is divided into four quadrants by a cruciform insulatingstructure.

4. The combination claimed in claim 3 wherein the extremities of saidinsulating structure are vacuum sealed to the hollow square cylindricalelectrode to form four vacuum separated monopole structures.

5. The combination claimed in claim 1 wherein said circular cylindricalelectrode is divided into two segments by an insulating structure.

6. The combination claimed in claim 5 wherein the extremities of saidinsulating structure are vacuum sealed to the hollow square cylindricalelectrode to form two vacuum separated monopole structures.

7. The combination claimed in claim 1 wherein said circular cylindricalelectrode is divided into three segments by an insulating structure.

8. The combination claimed in claim 7 wherein the extremities of saidinsulating structure are vacuum sealed to the hollow square cylindricalelectrode to form three vacuum separated monopole structures.

9. The combination claimed in claim 1 wherein said hollow squarecylindrical electrode forms part of a vacuum containment vessel for themass spectrometer.

10. The combination claimed in claim 3, wherein said means for applyingpotential is applied to each quad-' rant of the circular cylindricalelectrode.

1 1. The combination claimed in claim 5, wherein said means for applyingpotential is applied to each segment of the circular cylindricalelectrode.

12. The combination claimed in claim 7, wherein said means for applyingpotential is applied to each segment of the circular cylindricalelectrode.

13. The combination claimed in claim 1, wherein said square cylindricalelectrode is at a potential of zero.

1. A monopole mass spectrometer comprising: an analyzing configurationconsisting of a circular cylindrical electrode extending coaxiallywithin a surrounding hollow square cylindrical electrode; means forinjecting ionized beams into said spectrometer between said circularcylindrical electrode and said square cylindrical electrode; means fordetecting said beams disposed opposite said injecting means; and meansfor applying potential to both said circular cylindrical electrode andto said hollow square cylindrical electrode.
 2. The combination claimedin claim 1 wherein said circular cylindrical electrode is hollow.
 3. Thecombination claimed in claim 1 wherein said circular cylindricalelectrode is divided into four quadrants by a cruciform insulatingstructure.
 4. The combination claimed in claim 3 wherein the extremitiesof said insulating structure are vacuum sealed to the hollow squarecylindrical electrode to form four vacuum separated monopole structures.5. The combination claimed in claim 1 wherein said circular cylindricalelectrode is divided into two segments by an insulating structure. 6.The combination claimed in claim 5 wherein the extremities of saidinsUlating structure are vacuum sealed to the hollow square cylindricalelectrode to form two vacuum separated monopole structures.
 7. Thecombination claimed in claim 1 wherein said circular cylindricalelectrode is divided into three segments by an insulating structure. 8.The combination claimed in claim 7 wherein the extremities of saidinsulating structure are vacuum sealed to the hollow square cylindricalelectrode to form three vacuum separated monopole structures.
 9. Thecombination claimed in claim 1 wherein said hollow square cylindricalelectrode forms part of a vacuum containment vessel for the massspectrometer.
 10. The combination claimed in claim 3, wherein said meansfor applying potential is applied to each quadrant of the circularcylindrical electrode.
 11. The combination claimed in claim 5, whereinsaid means for applying potential is applied to each segment of thecircular cylindrical electrode.
 12. The combination claimed in claim 7,wherein said means for applying potential is applied to each segment ofthe circular cylindrical electrode.
 13. The combination claimed in claim1, wherein said square cylindrical electrode is at a potential of zero.